Fighting Carbine Optics: Pick the Right One

With optics ubiquitous on fighting rifles, the old rule that long barrels – with their longer sight radius – are needed for accuracy and longer-range capability is turned on its head. It’s possible to get one-moa mechanical accuracy from 18, 16, 14.5, 12.5, and even 10.5-inch barrels, perhaps at a higher cost. Thus, with even short-barreled CQB uppers able to provide pinpoint accuracy to the limit of the 5.56 cartridge’s capability- the role differentiation is determined by what optic is mounted on the rail. Put another way- carbine capability is determined by its sights.

The next problem is that…

there are five million optics sights on the market. Many are junk and need to be avoided. Others are good for hunting or target use, but not appropriate for a fighting rifle. Most are not suited well to the M4/M16 platform due to size, eye relief, or mounting issues. Finally, some organized thinking is required to figure out what capability and features you want in an optic to help, not hurt, yourself in getting your real job done.

I break down optics in basically three types for fighting carbines: Type I, Type II, and Type III. Type I is basically CQB. Type II is basically DMR. Type III is SPR.

Type I: 1x or non-magnified red-dot optics, optimized for close-range engagements and effective to the carbine’s point-blank range (250-300 yards for a M4/M16 with a 50-yard zero). Type I optics are heads-up, not sensitive to eye position, most are parallax-free. The most common Type I fighting optics are the Aimpoint M2-M4 and the EOTech. No magnification and heads-up binocular sighting provides the fastest sight-picture acquisition and the easiest to maintain while on the move. They are also the easiest to use from weird shoot positions. The downfall of the Type I optic is no magnification which hampers target ID (threat / no-threat). Iron sights still have a place due to bomb-proof mechanical simplicity, and fit in as a Type I sight.

There are two dominant Type I optics: the Aimpoint and the EOTech. The Aimpoint CompM2 (M68/CCO), CompM3, and CompM4 have much, much longer battery life than the EOTech. The Aimpoints also can be powered up and "verified on" by touch only, without looking at the reticle. The drill for turning on an EOTech is to hit the "on" button and keep hitting it while looking at the reticle until it’s bright enough. Market price for either of these optics including a quick-release mount is $500-800.

There are a couple "3x" magnifier units now becoming available which can be mounted just behind an Aimpoint or EOTech, yet be quickly flipped out of the way when not needed. These can help with target ID, however, they have a much narrower field of view than true magnified optics (Type II and III).

Type II: low-power magnified optics with reticle features for bullet-drop compensation when engaging targets outside of the cartridge’s point-blank range. External and non-capped target knobs/turrets should be avoided to ensure the zero is not lost when the knobs get bumped, hit, or rub on other gear. Type II optics are designed for quickly engaging targets from about 75 yards out to about 400 yards. Many Type II optics are fixed magnification at 3.5x or 4x, however, several variable power 1 – 4x scopes are also in use. The most common is the Trijicon ACOG: 4x (TA31, TA01) or 3.5x (TA11). The US Military realizes many of these needs in the Designated Marksman Rifle (DMR) and Squad Designated Marksman Rifle (SDM-R).

At CQB distances, most Type II optics are a liability– slower to acquire a sight picture than Type I red dots sights. The Type II optics can be used past 400 yards, however, targets must be large and the shooter will have to pay close attention to his particular weapon and ammunition’s performance when using the reticle BDC. These optics provide good target spotting and ID capabilities. Close-range performance can be improved if the optic provides a very bright center illumination such as Trijicon’s fiber-optic-lit "donut", taking advantage of the brains attraction to bright objects. Besides the fixed-power ACOGs, a low-variable-power Type II optic will improve close-range speed, giving close to 1x red dot acquisition speed, but the ability to crank up the power for target ID and longer shots.

Of the fixed-power Type II optics, the Trijicon ACOG TA11 is the best choice. It provides a little more eye relief and a large exit pupil than the TA01 and TA31. Together, these two attributes make it a lot faster to acquire a sight picture and easier to maintain while on the move. The 0.5x difference in magnification versus the TA31 is marginal. Price on a TA31 or TA11 ACOG with a QR mount is about a grand. The Schmidt and Bender 1.1-4x20mm Short Dot has almost true 1x at the low and a bright illuminated reticle center. It has a mil-based reticle for bullet drop, in addition to external target knobs (the locking turrets are the way to go for reliability). The extra capability of the Short Dot is paid for in bulk and its $2200 ticket. The sleeper is the 1.25-4x24mm Trijicon AccuPoint (TR21). It shares the same fiber-optic design as the TA31/TA11, but can be dialed down to low power for close-range work. Its reticle has no BDC features, however. The TR21 is a good deal at about $575.

Type III- the SPR scope. This type of optic has the capability to take the 5.56 cartridge to its ballistic limit and to engage small targets at extended distances. The 18-inch Mk12 Mod 1 SPR uses the Leupold 3-9x36mm M/RT, which was the first scope specifically designed for this role on the M4/M16 platform. The 5.56 cartridge is ballistically limited to 600 – 800 yards at sea level, so the Type III optic needs to be able to engage small targets at this distance. 5.56 has very little energy at this distance, however, 77-grain Mk262 has been used to make kills a over 600 yards. Besides long-range, the Type III optic has the ability to engage very small targets at intermediate ranges, which is a downfall of the Type II optic. When shooting at adversaries who are partially behind cover or wearing armor, being able to place a head-shot several hundred yards away can be key.

The Type III optic is most often a variable-power (approx. 3-9x) with external target turrets and reticle features which can be used for holdover in a hurry. The original M/RT is the canonical Type III optic for the M4/M16 platform. It was designed in a small form factor and with less eye relief to better fit the geometry of the carbine. Leupold has a couple other M/RT scopes now, including the 2.5-8x36mm. If you can deal with a large optical package, you can step into more conventional sniper scopes, such as the Leupold 3.5-10x40mm Mark 4 or the most excellent Schmidt and Bender 3-12x50mm PMII.

In conclusion- think carefully about your mission and likely engagement requirements, and then pick the type of optic that solves those problems best. The Type I one-power red dot sight is the right choice for the vast majority of fighting with a carbine. The Type II is more specialized yet brings some useful capabilities to the table, whereas the Type III is really a very specialized application. Whatever you choose for your mission- get one of the solid battle-proven optics mentioned here. There’s a lot of junk out there that will let you down sooner or later.

About David Crane

David Crane started publishing online in 2001. Since that time, governments, military organizations, Special Operators (i.e. professional trigger pullers), agencies, and civilian tactical shooters the world over have come to depend on Defense Review as the authoritative source of news and information on "the latest and greatest" in the field of military defense and tactical technology and hardware, including tactical firearms, ammunition, equipment, gear, and training.